The present invention relates to an apparatus for irradiating a sample by an electromagnetic beam, preferably a pulsed laser beam, and for performing a subsequent mass analysis of the ions generated by the irradiation. The apparatus includes a microscope for focusing the laser beam as well as for observing the sample, and further has a mass spectrometer and illuminating means operatively coupled to the sample in a selective manner.
An apparatus of the above-outlined type serves primarily to examine thin sections for physiological and biomedical uses, but is suitable as well for analyzing any other type of thin samples. It is a particular advantage of such an apparatus that extremely small sample zones (for example, in the order of magnitude of cell components of biological substances) can be irradiated and analyzed. In order to be able to direct the laser beam to such small sample zones and to correlate the locus of analysis with the morphologic structure of the sample, the latter has to be observed with a microscope, particularly in transillumination. Moreover, devices for setting interference, phase and polarization contrasts and the like are desirable. Thus far, however, meeting the requirement of an examination by microscope has, in practice, encountered considerable difficulties, since the means for transillumination as well as the entrance opening of the means for mass analysis of the ions must be located very close to the sample. For this reason transillumination of the sample has often been renounced and only reflected illumination means were provided. In reflected light, however, cells disposed in a sample section are very difficult to distinguish.
German Pat. No. 2,141,387 discloses an arrangement which includes a monitor, an illumination device, a mass spectrometer and a device for observing luminescence. These devices are mounted together on a turret and thus can be selectively swung into an operating position. Such a device, however, involves prohibitive manufacturing costs, particularly if-- as it is often the case-- a time-of-flight tube of more than 2 m long is used as the mass separating system and if all these devices must be disposed in a vacuum chamber. Time-of-flight spectroscopy, in particular, has been found to the especially suitable for the examination of organic samples by laser beam irradiation not only because of the high resolution and a high probability of detection, but primarily because the total element information is available immediately after each laser bombardment.
The periodical "Analusis", in issue No. 3 of 1976, on pages 115-119 discloses a pivotal prism which can be swung into its operating position for directing the light required for transillumination onto the sample from a light source disposed outside the mass spectrometer. In this device, the essential lens systems are also disposed outside the mass spectrometer, that is, relatively far from the sample, so that a greatly enlarged observation of the sample in transillumination is not feasible.